Peeled Films Research Articles

3D cell sheets formed via cell-driven buckling-delamination of patterned thin films

Complex geometries such as folds and protrusions in various organs are formed by the wrinkling/buckling of flat epithelial sheets. This morphogenesis is considered to be triggered by mechanical instabilities between the epithelial sheet and the mesenchyme foundation, similar to that observed in non-living film-on-substrate structures. Here, we report a film-on-substrate cell culture system (FoSS), in which the cells can induce wrinkling and buckling-delamination of the surface layer from the foundation. Ion beam irradiation on polylactic acid (PLA) produced three layers: a crosslinked/carbonized surface, a decomposed middle layer that undergoes solation under the cell culture condition, and a foundation. This system was realized by controlling the three-dimensional (3D) distributions of scission/crosslinking probabilities in PLA. Madin-Darby canine kidney epithelial cells adhered well to the surface layer of FoSS. Cellular forces caused the layer to become wrinkled and subsequently delaminated as a thin film (~165 nm) from the foundation. The cell population then crumpled the peeled films, and within 48 h formed 3D cell sheets with folds and protrusions depending on patterns pre-set on the FoSS. FoSS can be utilized to produce in vitro models of 3D morphogenesis and 3D cell sheets that are currently in demand for tissue engineering and regenerative medicine.

Recovery Method of Pyrolytic Carbon Surface after Exposure to Chlorine Trifluoride Gas

An annealing process was developed for the practical recover of a purified py-rolytic carbon (PPyC) surface from damage, such as color change and peeling, due to fluorination during exposure to chlorine trifluoride gas at high tempera-tures for the cleaning of a silicon carbide chemical vapor deposition reactor. The PPyC surface was annealed at 900°C for 10 min in ambient nitrogen con-taining oxygen at the concentrations of 0.01% - 20%. The rainbow-like colored surface returned to the dark gray color of the original PPyC. Simultaneously, the thin peeled films disappeared. The Raman spectra showed that the PPyC surface chemical bonding returned to that of the original one. The oxygen concentration as low as 0.01% could recover the PPyC surface along with re-ducing the surface pit formation, when the combination of the exposure to chlorine trifluoride gas and the recovery was repeated.

Static and Dynamic Hydrophobic Properties of Honeycomb Structured Films via Breath Figure Method

This work reported the static and dynamic hydrophobic properties of the honeycomb porous and peeled films with pincushion structures by changing the concentrations of the copolymer solution. Honeycomb porous films were fabricated via breath figure technology employing a pentablock copolymer containing poly(ethylene glycol)/PEG, poly(methyl methacrylate)/PMMA, and poly(trifluoroethyl methacrylate)/PTFEMA. The relationship between the copolymer concentrations and the pore size (D) and rim width (W) was examined. Moreover, we studied the hydrophobic properties from different surfaces of flat, porous, and pincushion structures, and the contact angles, W/D ratios, and fraction of air on the porous and pincushion films were obtained. It was noteworthy that the W/D ratios and surface hydrophobic properties had a notable correlation. Finally, the dynamic behaviors of water droplets impacting on these porous and pincushion films were examined using a high speed camera. It examined the influence of the fraction of ...

Polarization dependence of thermo-optic coefficients in polyimide films originating from chain orientation and residual thermal stress

Control of polarization dependences of thermo-optic (TO) coefficients, i.e., the temperature dependence of birefringence (d(Δn)/dT), is critical issue for optical materials. Especially in active optical components like TO switches, polarization dependent behaviors are caused by d(Δn)/dT of materials. Origins of polarization dependence of TO coefficient were investigated for seven kinds of polyimide (PI) films in terms of main chain orientation and residual thermal stress. The values of d(Δn)/dT of PI films originated from chain orientation vary from nil to negative as the degrees of in-plane orientation increase. Magnitudes of d(Δn)/dT depend on intrinsic birefringences, second order orientation coefficients, and their temperature dependence. On the other hand, those of d(Δn)/dT originated from residual stress are negative for PI films exhibiting large in-plane coefficients of thermal expansion (CTE) and vary to zero as their CTE decreases due to reduced residual stress. d(Δn)/dT originating from chain orientation decreases as the degree of chain orientation increases, but that from residual thermal stress increases, which is the reason that no apparent trend was observed for the d(Δn)/dT of PI films adhering to Si substrates. Based on these examinations, the d(Δn)/dT of on-substrate PI films were successfully decreased to the levels of peeled PI films by incorporation of alicyclic structures in the main chains and/or the use of PI substrates whose CTEs are close to those of PI films.

Effect of Ar+ Radiofrequency Plasma Treatment Conditions on the Interfacial Adhesion Energy Between Atomic-Layer-Deposited Al2O3 and Cu Thin Films in Embedded Capacitors

The effects of Ar+ radiofrequency (RF) plasma pretreatment conditions on the interfacial adhesion energy of a Cu/Cr/Al2O3 system were investigated for thin-film capacitors in embedded printed circuit board applications. The interfacial adhesion energy was evaluated from 90 deg peel tests by calculating the plastic deformation energy of peeled metal films from the energy balance relationship during the steady-state peeling process. The interfacial adhesion energy was fivefold higher after RF plasma pretreatment of the surface of 50-nm-thick Al2O3 prepared by atomic layer deposition. Atomic force microscopy, Auger electron spectroscopy, and x-ray photoemission spectroscopy results clearly reveal that this increase can be attributed to both mechanical interlocking and chemical bonding effects.

Multilayer films using polypropylene/polypropylene grafted with acrylic acid blends and polyamide 6

Blends of polypropylene (PP) with 0 to 100 wt% of polypropylene grafted with acrylic acid (AA-g-PP) were used to promote the adhesion to polyamide 6 (PA 6) in a three-layer coextruded film without using an additional adhesive or tie-layer. The effect of modified polymer content and its molecular weight on interfacial adhesion between PP and PA 6 was determined by T-peel strength measurements. The effect of melt temperature and bonding time on peel strength was determined. Oxygen and water vapor transmission rates of the films were measured. The peel strength of fusion bonded layers of PP/AA-g-PP blends with PA 6 strongly depends on bonding temperature and time, as well as on the molecular weight of the functionalized polymer. The peeled films surfaces were characterized using FTIR-ATR and scanning electron microscopy (SEM). Tensile properties of three-layer films, made up of PA 6 as the central layer and PP/AA-g-PP blends as the two external layers, are improved with increase in the acrylic acid (AA) content in the blend. The formation of an in situ copolymer between AA in the blend and the terminal amine groups of PA 6 was confirmed by the Moalu test.

Cohesive failure of the Cu/polyimide system

The cohesive failure which occurs in the inside of the polymer near the metal/polymer interface was studied in the Cu/Cr/polyimide and Cu/CuCr/polyimide systems. The interface energy was varied by pretreating the polyimide surface by varying rf plasma power density, or by varying the Cr content in the CuCr alloy layer, respectively, and peel tests were conducted. Then, peeled metal strips were analyzed by AES and XPS, and correlations were made among the peel strength, the amount of carbide-like Cr–C bonds near the interface, and the polyimide thickness on peeled metal films inferred from the AES depth profiling. Results indicate that the peel strength increased with the rf power density at a constant metal thickness and that the thickness of polyimide adhering to peeled metal films increased with the peel strength, which was related to the amount of carbide-like CrC bond near the interface affecting the interface energy. In the case of specimens with the same plasma treatment but various metal layer thickness, the thickness of polyimide on peeled metal films remained constant even though the peel strength increased with the metal layer thickness.

An X-ray study on the mechanical effects of the peel test in a Cu/Cr/polyimide system

In order to understand the effects of plastic deformation and the interfacial fracture energy on the peel strength, thickness of the metal layer and the pretreatment conditions of polyimide were varied in the Cu/Cr polyimide system. The work expenditure during the peel test was estimated using the stress–strain curves of metal films, X-ray measurements of the plastic strain in peeled films, and the elastoplastic beam analysis. Results indicate that the peel strength is strongly affected by the film thickness and the pretreatment condition in a synergistic way, and that the peel strength shows a maximum at an intermediate thickness level. The estimated work expenditure was close to measured peel strength for most of the cases, which indicates that the measured peel strength is more a measure of the plastic deformation during the peel test than a measure of the true interfacial fracture energy.

Performance of multilayer films using maleated linear low‐density polyethylene blends

AbstractBlends of linear low‐density polyethylene (LLDPE) and linear low‐density polyethylene grafted maleic anhydride (LLDPE‐gMA) were prepared by melt mixing and then coextruded as external layers, with a central layer of polyamide (PA) on three‐layer coextruded flat films. Blends with contents of 0% to 55 wt% of maleated LLDPE, on the external layers, were analyzed. The T‐peel strength and oxygen and water vapor transmission rate of the films were measured. The surfaces of the peeled films were characterized using attenuated total reflection infrared spectroscopy (FTIR‐ATR) and scanning electron microscopy (SEM). The observed increase in T‐peel strength of the films with 10% and higher levels of maleated LLDPE in the blend suggests good interfacial adhesion between layers. This sharp increase in peel strength appears to be associated, besides interdiffusion, with specific interactions between polymers, as the bond formation between maleic anhydride and the polyamide end groups by in situ block copolymer formation across the interface. No significant modifications in oxygen barrier properties of the films were observed; however, the use of higher contents of LLDPEgMA, even though it increases the adhesion performance, also increases the water vapor transmission rate by a reduction in the degree of crystallinity.

Peel Strength in the Cu/Cr/Polyimide System

AbstractIn order to understand the effects of plastic deformation and the interfacial fracture energy on the peel strength, thickness of the metal layer and the pretreatment conditions of polyimide were varied in the Cu/Cr/polyimide system. The work expenditure during the peel test was estimated using the stress strain curves of metal films, X-ray measurements of the plastic strain in the peeled films, and the elastoplastic beam analysis. Results indicate that the peel strength is strongly affected by the film thickness and the pretreatment condition in a synergistic way, and that the measured peel strength is more a measure of the plastic deformation during the peel test than a measure of the true interfacial energy.

On the mechanism of the emission of high-energy electrons from the surfaces of freshly peeled films: Polytetrafluoroethylene

This paper describes the results of an investigation of high-electron emission accompanying the mechanical disruption of adhesive contact in vacuo. Investigations of such emission parameters as the energy of the electrons, their angular distribution, depth of the electron capture center levels on freshly formed polymer surfaces responsible for the emission as well as the establishment of relations governing the time variation of the parameters of the emitted electrons' flux, their relation to the polymer film surface charge, and finally the numerical computations based on these experiments have led the authors to the conclusion that the mechanism of electron emission from freshly formed polymer film surfaces has a field-emission nature proceeding from surface states and is described accurately enough by the analytical expressions derived from the above considerations.

Temperature and humidity effects on adhesion of polyimide film to a silicon substrate

A 90° peel tester with substrate heating capability was built to evaluate the adhesion strength of polyimide films to a silicon substrate. The effects of polyimide film thickness and peel rate on polyimide adhesion to a silicon substrate under high or low humidity, and at elevated temperatures, have been evaluated. In a high humidity environment, a low peel strength was measured. The influence of moisture on the peel strength increases with decreasing peel rate. Peeling at elevated temperature reduces the moisture effect even under high humidity conditions. Using a low peel rate in a high humidity environment, the measured peel strength showed a maximum as the polyimide film thickness increased. No striations in peeled polyimide films were observed for peeling in a high humidity environment.

A Calorimetric Evaluation Of The Peel Adhesion Test

ABSTRACTSimultaneous mechanical and calorimetric measurements of the work and the heat of peeling have been made for polyester films bonded to rigid metal substrates with a pressure sensitive adhesive. Most of the work expended in peeling is consumed by plastic deformation and viscous dissipation. 70% to 85% of the peel energy is dissipated as heat. The peeled polyester films were tightly curled. Energy stored in the peeled polyester films was measured using solution calorimetry and a significant fraction of the peel energy not dissipated as heat was found to be stored in the peeled films.

An x-ray photoemission spectroscopy study of chemical interactions at silver/plasma modified polyethylene interfaces: Correlations with adhesion

Plasma treatment is a convenient way to modify the surface (∼25–50 Å) of a polymer for improved adhesion of vacuum deposited metals. X-ray photoemission analysis of plasma modified polyethylene (PE) indicates no detectable chemical effects for argon plasmas, whereas oxygen and nitrogen plasmas create new chemical species which alter the chemical reactivity of the PE surface for vacuum deposited Ag. The adhesion strength of vacuum deposited Ag on PE is shown to increase in the following order: untreated<argon plasma<oxygen plasma<nitrogen plasma treated PE. Changes in chemical bonding and nucleation of submonolayer vacuum deposited Ag on plasma treated PE correlate with Ag/PE adhesion. Changes in the PE core levels after submonolayer deposition of Ag are interpreted as due to the formation of Ag–O–C and Ag–N–C species on oxygen and nitrogen plasma treated PE, respectively. In contrast, no chemical bonding effects are observed on untreated or argon plasma treated PE. The Ag valence-band structure suggests that the plasma induced species act as nucleation and chemical bonding sites resulting in a much smaller average cluster size for vacuum deposited Ag. Interfacial analysis of peeled thin films of vacuum deposited Ag on PE suggests the locus of failure changes from interfacial adhesive failure for untreated and argon plasma treated PE to cohesive failure of the PE for oxygen and nitrogen plasma treated PE.

On the mechanism of the emission of high-energy electrons from the surfaces of freshly peeled films: Polytetrafluoroethylene

This paper describes the results of an investigation of high-electron emission accompanying the mechanical disruption of adhesive contact in vacuo. Investigations of such emission parameters as the energy of the electrons, their angular distribution, depth of the electron capture center levels on freshly formed polymer surfaces responsible for the emission as well as the establishment of relations governing the time variation of the parameters of the emitted electrons' flux, their relation to the polymer film surface charge, and finally the numerical computations based on these experiments have led the authors to the conclusion that the mechanism of electron emission from freshly formed polymer film surfaces has a field-emission nature proceeding from surface states and is described accurately enough by the analytical expressions derived from the above considerations.

Range in tungsten of Ba-140 fragments from the thermal neutron-induced fission of enriched uranium

Differential range measurements in tungsten were made on Ba-140 and Sr-91 fragments produced in the fission of thin samples of enriched uranium irradiated in the Puerto Rico Nuclear Center research reactor. Thin, uniform films of enriched uranium approximately 60 μg/cm 2 thick were deposited on stainless steel disks using an electrolytic technique developed by one of us. An electrolytic “peeling” method similar to that developed by McCargo et al. was used to remove thin surface films of tungsten oxide containing fission product activities. The fragments of interest were then isolated from the peeled films in radiochemically pure condition. A value of 7·68 ± 0·15 mg/cm 2 was observed for the most probable range of Ba-140. Values of 9·0 ± 0·2 and 11·3 ± 0·3 mg/cm 2 were observed, respectively, for the extrapolated range and the maximum penetration depth of the fragment. The experimental value for the range of Ba-140 is in good agreement with range values calculated from semi-empirical relations recently developed by Noshkin and Sugihara and Mukherji and Yaffe.